Thursday, March 6, 2014

Migration of MTR suites to use InnoDB (continued …)

This is a continuation of my post on migration-of-mtr-suites-to-use-innodb . To set the context here is a quick recap.
MySQL 5.5 had the following changes with respect to the default engine

Default engine in the server changed from MyISAM to InnoDB

MTR modified to start server with the old default MyISAM. (This was
required because historically most test results were recorded with
MyISAM and many of them would fail if tests were run with the new server
default, InnoDB)

Tests retained as is in 5.5 and planned to migrate them to run with default engine in a future release

In MySQL 5.7 release we have started the migration project. Right in
the beginning we realized that the switch of default engine had an
unexpected side effect. MTR tests that were developed post 5.5 were also
getting recorded and run with MyISAM unless an engine was explicitly
specified in the test. I.e. we were in a state where not only old
tests, but also new tests were running with the old default engine
MyISAM. As a result the backlog of tests that had to be migrated was
growing over time. We decided to fix the problem with new tests first
and old tests later.

The only way we could force new tests to run with InnoDB by default
was to remove the engine switch in MTR. This however would bring back
the problem of existing tests failing with result difference. We decided
to tackle this problem with a different approach. Instead of switching
the engine in the test tool itself, it was switched in the existing
tests. This is where the force_myisam_default.inc makes its entry. If
this file is included it will tell MTR to start server with MyISAM. It
was added to all existing tests that did not have any explicit engine
specification at the test level. To be more precise it was added to
tests that did not have have_innodb.inc, have_archive.inc etc. We then
removed the switch in MTR, so that by default it starts the server with
its default engine which is InnoDB. With these 2 changes we got to the
state where new tests by default were running with InnoDB.This was a big
step forward and on hindsight I think we should have done this instead
of the engine switch in 5.5 .

Having fixed the problem with new tests, we have now shifted our
focus to migration of old tests. The migration project does not in any
way reduce the test coverage on MyISAM; rather it just adds InnoDB
coverage where it was missing. Post migration tests for features which
are dependent on the engine will have MyISAM and InnoDB variants. Tests
for features that are expected to have same behavior on all engines may
run only with the default engine InnoDB.
We have outlined following strategy for the migration project:

Maintain MyISAM and innodb variants for tests and subtests that are dependent on the engine

Remove MyISAM dependencies from tests that are not meant for testing MyISAM features

Retain tests for MyISAM only features in MyISAM

There is an element of risk in this project since any small mistake
can lead to missing or even worse wrong tests. However be rest assured
that this is being handled with utmost care by our strong QA team. To
ensure correctness and stability all result differences are analyzed and
discussed with the concerned people before making any changes. Some of
the differences were due to bugs and these are fixed before test
migration. Some others are expected and are accepted as they are. Listed
below are a few examples of the changes made to the result files:

As of 5.7.3 release migration is complete for auth_sec, federated,
funcs_1, funcs_2, jp, opt_trace, perfschema, stress and sys_vars suites.
It is not all done yet and you will see more and more tests getting
migrated in the upcoming milestone releases.

If you have any questions or feedback regarding this project please
post them here. I would love to hear what the community thinks about
this.